Epitaxial crystallization of polyethylene on graphite

Tuinstra, F.; Baer, E.

doi:10.1002/pol.1970.110081205

Cited by 68 publications

(58 citation statements)

References 3 publications

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“…48 A schematic representation of tetradecane adsorbed on graphite is shown in Figure 2 for illustration. 57 Investigations of PE-crystallization 58 via electron microscopy from highly diluted solutions on graphite confirmed the existence of attractive interactions between PE and the graphite substrate. Due to these interactions, orientation of PE chains at crystallization upon the graphite is oriented (so-called epitaxial crystallization).…”

Section: Resultsmentioning

confidence: 82%

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Macko¹,

Brüll²,

Wang

et al. 2011

J of Applied Polymer Sci

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Blends of linear polyethylene (PE) and isotactic polypropylene (iPP) with different average molar masses and a series of ethylene-propylene (EP) copolymers with different chemical composition as well as blends of PE, Ipp, and EP copolymers were separated using a carbon-column packing (HypercarbV R ) and gradients of 1-decanol or 2-ethyl-1-hexanol ! 1,2,4-trichlorobenzene (TCB). The separation is based on full adsorption of linear PE on the carbon sorbent at temperature 160 C. However, iPP is not adsorbed and elutes in size exclusion mode. The random EP copolymers have been adsorbed in the column packing and separated according to their average chemical composition after application of the gradient starting with alcohol and ending with pure TCB. The elution volumes of the copolymers depended linearly on the average concentration of ethylene in the copolymers. The HPLC elution profiles were correlated with the CRYSTAF elution profiles. In contrast to CRYSTAF, fully amorphous polyolefin samples were separated with the high-temperature adsorption liquid chromatography.

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Section: Resultsmentioning

confidence: 82%

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Macko¹,

Brüll²,

Wang

et al. 2011

J of Applied Polymer Sci

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“…It is well-known that PE crystallizes epitaxially on graphite (29). Standard differential scanning calorimetry (DSC) measurements of PE with graphite added in pulverized form confirm that the latter also initiates crystallization in bulk, because the crystallization temperature observed during cooling is raised (Fig.…”

Section: Resultsmentioning

confidence: 98%

Direct observation of prefreezing at the interface melt–solid in polymer crystallization

Löhmann

Henze

Thurn‐Albrecht

2014

Proc. Natl. Acad. Sci. U.S.A.

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Crystallization is almost always initiated at an interface to a solid. This observation is classically explained by the assumption of a reduced barrier for crystal nucleation at the interface. However, an interface can also induce crystallization by prefreezing (i.e., the formation of a crystalline layer that is already stable above the bulk melting temperature). We present an atomic force microscopy (AFM)-based in situ observation of a prefreezing process at the interface of a polymeric model system and a crystalline solid. Explicitly, we show an interfacial ordered layer that forms well above the bulk melting temperature with thickness that increases on approaching melt-solid coexistence. Below the melting temperature, the ordered layer initiates crystal growth into the bulk, leading to an oriented, homogeneous semicrystalline structure.semicrystalline polymers | AFM | thin films | epitaxy T he fundamental process of crystallization from the liquid or gaseous state is of importance in many areas of condensed matter physics and materials science. In practice, crystallization is, in most cases, initiated at an interface to a solid. Crystal growth on solid substrates from the gaseous state has been studied in depth, and detailed understanding of different growth modes as well as interfacial thermodynamics has been achieved (1-3). Much less experimental data are available for crystallization occurring at the interface from the solid to the melt. Generally, crystallization can be initiated at the solid-melt interface by two processes: heterogeneous nucleation or formation of a crystalline wetting layer (so-called prefreezing) (4-6). In terms of thermodynamics, these processes are very different. Whereas nucleation takes place under nonequilibrium conditions at finite supercooling below the melting temperature T m of the bulk material, the formation of a wetting layer is an equilibrium phenomenon taking place above T m (4). It is often assumed that heterogeneous nucleation is the more relevant process (7), but in simulations, nucleation as well as prefreezing have been shown to occur (4,8). Prefreezing is expected for strongly attractive surfaces or epitaxial systems for which the lattices of the substrate and the crystallizing materials match well (9-12). In the case of polymers, prefreezing can also manifest itself in the conformational degrees of freedom, leading to an interfacial layer with nematic order, which was recently shown in simulations (13). Because of the difficult accessibility of the buried interface between a melt and a solid, direct observation of crystallization of molecular systems at the interface is lacking, and there is only limited, indirect evidence that, in some cases, prefreezing at the solid interface exists (e.g., for the growth of aluminum crystals on TiB 2 particles) (14, 15). Recently, it has been suggested that prefreezing also plays a role during epitaxial crystallization in some polymeric systems (16). It is well-known, however, that one or sometimes several ordered layers of organ...

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“…It is well known that the epitaxial growth of polymer crystals on inorganic substrates can proceed at temperatures which are above the homogeneous crystallization threshold in solution. [22,23] The EM images of epitaxially grown lamellae and so called featureless ''contact layer'' have been obtained for polyethylene crystallized from xylene on alkali halides at temperatures up to its dissolution temperature [22] or even exceeding this temperature at growth on graphite. [23] This fact can be regarded as an indication that polymer molecules adsorbed on a crystal surface adopt folded states at anomalously high temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…[22,23] The EM images of epitaxially grown lamellae and so called featureless ''contact layer'' have been obtained for polyethylene crystallized from xylene on alkali halides at temperatures up to its dissolution temperature [22] or even exceeding this temperature at growth on graphite. [23] This fact can be regarded as an indication that polymer molecules adsorbed on a crystal surface adopt folded states at anomalously high temperatures. Alternatively, we may assume that nanocrystallites have been formed at deposition stages with lower temperatures subsequent to dipping.…”

Section: Resultsmentioning

confidence: 99%

Direct Observation of Poly(propylene)‐block‐Poly(ethylene‐co‐propylene) Molecules by Atomic Force Microscopy

Прохоров¹,

Nitta

Terano

2004

Macro Chemistry & Physics

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Summary: Atomic force microscopy (AFM) has been applied to get molecular images of diblock poly(propylene)‐block‐poly(ethylene‐co‐propylene) copolymers deposited on mica from diluted solutions at elevated temperatures. Both isolated molecules and their small aggregates have been visualized as compact particles of various sizes with outspreading poly(ethylene‐co‐propylene) chains. On the base of the height, volume and morphological analysis AFM images were divided into three groups. In the first group the compact particles are suggested to be small regular‐shaped crystallites formed by a few poly(propylene) blocks. Some isolated particles of this group were connected with single copolymer chains. In the second group the compact particles have larger dimensions and irregular or round shapes implying unordered packing of constituents. The third group were represented by isolated poly(ethylene‐co‐propylene) coils. The two‐dimensional expansion of coils on mica both isolated and included in aggregates exceeds several times their dimensions in a solution. The probable mechanism of such an expansion is proposed relying on the existence of van‐der‐Waals surface force field of a sufficient strength in the vicinity of the crystal surface.Enlarged AFM height images of block‐copolymer aggregates of group A with small compact particles of regular shapes (frames a, b, c) and group B (frame d) with a large globular compact particle.imageEnlarged AFM height images of block‐copolymer aggregates of group A with small compact particles of regular shapes (frames a, b, c) and group B (frame d) with a large globular compact particle.

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Epitaxial crystallization of polyethylene on graphite

Cited by 68 publications

References 3 publications

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Direct observation of prefreezing at the interface melt–solid in polymer crystallization

Direct Observation of Poly(propylene)‐block‐Poly(ethylene‐co‐propylene) Molecules by Atomic Force Microscopy

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